The overall goal of this project is to understand how opioids and the neuropeptide, substance P (SP), operate as central mediators in the interaction between the immune system and the nervous system and in the immunopathogenesis of HIV infection and AIDS. Our overarching hypothesis is that SP and the SP receptor(neurokinin-1 receptor, NK-1R) are biologically involved in opioid- or opioid withdrawal-mediated immune modulation related to the immunopathogenesis of HIV infection and AIDS. We predict that SP levels in the circulating blood and peripheral tissues increase as a result of opioid abuse, which results in immune suppression and enhanced HIV infection of the human immune cells and that opioid withdrawal accentuates this effect. In our ongoing studies (DA12815), we have demonstrated that opioid-dependent subjects attending a methadone treatment program have increased levels of circulating plasma SP and expression of SP mRNA in PBMC in comparison to normal subjects. These unique and novel observations constitute a compelling rationale for the continuation of our studies characterizing the role of opioids and/or SP in the immunopathogenesis of HIV infection and AIDS. Furthermore, these findings provide the basis for new detailed mechanistic studies into the biologic interaction between opioids and SP in the CNS and human immune systems. In Aims 1-2, we propose new in vitro studies that will extend our existing in vitro models using cells from the human immune system and CNS in order to investigate the interaction between opioids, SP and HIV. These new in vitro studies will provide physical evidence as well as insight into the molecular mechanisms of the interaction of opioids and/or SP with HIV in both human immune and CNS cells. The impact of opioid withdrawal on the expression of SP and NK-1R, as well as the immune function related to HIV infection, also will be a new focus of the proposed study. We propose new ex vivo studies (Aim 3) to examine the role of opioids and/or SP in suppression of host innate immunity against HIV infection and in the activation of HIV in latently-infected immune cells. We will further characterize the in vivo relationship between opioids, SP and immune function using specimens from HIV + and HIV opioid-dependent subjects(Aim 4a). In addition, we will examine the role of in vivo opioid withdrawal in modulation of immune cell function, the expression of SP/NK-1R and HIV/HCV viral loads (Aim 4b). The proposed studies represent a unique series of experiments directed toward elucidating the host defense processes and the role of opioids abuse in HIV infection of human immune cells as well as in HCV infection, which will ultimately further the design and development of improved treatment regimens for substance-abusing subjects. [unreadable] [unreadable] [unreadable] [unreadable]